Conventional scissors require frequent resharpening, especially in demanding professional use. This calls for scissor disassembly, grinding and reassembly--a costly process, requiring special skills. With unconventional scissors such as described in the U.S. Pat. No. 5,014,433, this is even more complicated, if possible at all, due to multiple joints which may even comprise rolling bearings.
Another problem of scissors is the control of the normal contact force at the edge-to-edge crossing point which moves with closing of the scissors from near the pivot point of the two cutting blades to their tips. A certain contact force is necessary for reliable cutting. This is usually achieved by bending of the blades (if made from sheet metal) or grinding (if forged or cast), in such a way that blade edges push against each other as the scissors are closed. Bending compliance of the blades increases with the third power of the distance from the pivot point. To keep the force between the blade edges approximately constant, they must be bent more towards the tip, but very little near the pivot point. In practice, edge-to-edge contact force near the pivot is controlled by the assembly of the pivot. Any loosening at the pivot will cause a poor function of the scissors at the beginning of the cut when they are near fully opened.
Different types of modular scissors with removable blades are already known; the need for them came with the use of ceramic materials for the cutting blades. These are highly priced professional tools used mostly to cut high strength fibers (carbon, kevlar, glass). However, in these known scissors the whole blade is made in ceramic and is fixed directly to the handle. The disadvantages of this design is that the whole blade has to be replaced which is costly.